1. Field of the Invention
The present invention relates to a method of mounting a semiconductor device to a substrate and a mounted structure thereof and, more in particular, to a method of mounting a semiconductor device to a substrate by a flip-chip system and a mounting structure thereof.
2. Description of the Related Art
Accompanying with reduction in the size and lowering of the cost in electronic equipments in recent years, a structure for mounting semiconductor devices on a substrate at a high density has been simplified. A flip-chip system has been proposed as a high density mounting structure of semiconductor devices having such a simplified structure.
In the flip-chip system, a semiconductor device with a plurality of bump electrodes being mounted to at least one surface thereof is connected to a circuit substrate with the surface being faced downward, which is disclosed in Japanese Patent Laid-Open Hei 4-82241. Now, the conventional flip-chip mounting structure will be described with reference to FIG. 1.
Referring to FIG. 1, an insulating resin layer 2 made of a material such as rubber having elastic recovery force is formed on a substrate 1. Further, a mounting pad 3 is formed on the insulating resin layer 2 by means of sputtering or vapor deposition. A sealing resin 5 is coated to a region on the insulating resin layer 2 in which a semiconductor device 4 is mounted to the substrate 1. On the other hand, a plurality of bump electrodes 6 are formed to the surface of the semiconductor device 4 facing the substrate 1.
In the manufacturing method of the conventional mounting structure, at first, a plurality of the bump electrodes 6 disposed on the lower surface of the semiconductor device 4 and the mounting pad on the substrate 1 are aligned and then the semiconductor device 4 is bonded under pressure on the substrate 1. In this case, since the sealing resin 5 between the bump electrode 6 of the semiconductor device 4 and the mounting pad 3 on the substrate 1 is extruded, the bump electrode 6 and the mounting pad 3 are connected electrically with each other. In this conventional flip-chip mounting structure, since the insulating resin layer 2 having the elastic recovery force is formed between the substrate 1 and the mounting pad 3, electric connection between the bump electrode 6 and the mounting pad 3 can be held stably by the elastic recovery force of the insulating resin layer 2 and the contracting force of the sealing resin 5.
However, in the conventional flip-chip mounting structure, the elastic recovery force of the insulating resin layer 2 or the contracting force of the sealing resin 5 tends to suffer from degradation in an accelerated test such as a temperature cycle test and, as a result, the amount of heat expansion of the sealing resin 5 is greater than the contracting force thereof and the elastic recovery force of the insulating resin layer 2, to form a gap between the bump electrode 6 and the mounting pad 3. Accordingly, the gap formed between the bump electrode 6 and the mounting pad 3 causes connection failure between the semiconductor device 4 and the substrate 1.
Further, in the conventional flip-chip mounting structure described above, the semiconductor device 4 and the substrate 1 are connected in a state where the mounting pad 3 and the insulating resin layer 2 are deformed elastically. Accordingly, when the balance between the contracting force of the sealing resin 5 and the elastic recovery force of the insulating resin layer 2 should change by the temperature change, the deformed state of the mounting pad 3 changes correspondingly. Thus, considerable stresses exert on the mounting pad 3 due to temperature change and, as a result, the mounting pad 3 is damaged to sometimes cause disconnection or the like.
Further, in the conventional flip-chip structure, since it is necessary to form the insulating resin layer 2 having the elastic recovery force on the substrate 1, it cannot avoid the complexity for the production step and increase of the production cost.
It is an object of the present invention to provide a method of mounting a semiconductor device to a substrate and a mounted structure thereof, capable of improving the reliability in a connected state.
It is another object of the present invention is to provide a method of mounting a semiconductor device to a substrate and a mounted structure thereof capable of maintaining a stable connection state to the increase of temperature or change of circumstantial temperature.
To achieve the above objects, the structure for mounting a semiconductor device to a substrate comprises a mounting pad disposed on the substrate, a sealing resin provided on the substrate on which the semiconductor device is to be mounted, and a plurality of projecting electrodes disposed on a surface of the semiconductor device facing the substrate, and each of the projecting electrodes including a substantially spherical portion and a pointed portion in contact under pressure with the mounting pad and deformed such that a contact portion with the mounting pad is enlarged from a point to a plane.
Further, to achieve the above objects, the method of mounting a semiconductor substrate having a plurality of projecting electrodes to a substrate, on which a mounting pad is formed and an sealing resin is provided, wherein the method comprises the steps of pressing the projecting electrode to the mounting pad and thereby deforming a pointed shape portion at the top end of each the projecting electrode and, hardening the sealing resin.